Deepwater drilling is the exploration and extraction of petroleum and natural gas at depths of several thousands of feet (appx. one thousand meters) as of 2011. Offshore oil drilling began commercially in the 1890s and, by the early 1970s, the first wells exceeding 1,000 feet (305 meters) in depth were drilled. In the early 21st century, drilling began to reach multiple thousands of feet, and a new term for drilling depth known as ultra-deepwater, meaning 5,000 feet (1,524 meters) or more, became a practical reality. As of April 2011, the world record for the successful deepwater drilling of a functional offshore oil well was 10,194 feet (3,107 meters) set by drillships along the coast of India. This is superseded, however, by a borehole, a completed well that was not yet being fully tapped for oil or natural gas at the time off the coast of the Russian island of Sakhalin in January 2011 that reached a depth of 40,502 feet (12,345 meters).
Both oil exploration and gas exploration deepwater drilling have only become feasible in the 21st century for several key reasons. Primary among these is the rising price for fossil fuel commodities on the world market as of 2007 to 2008, as well as advances in technology that have made the practice more proven. Rising oil and gas prices are considered to be the direct cause for an increase in deepwater drilling oil rigs in the Gulf of Mexico that went from three rigs in 1992 to a total of 36 operational rigs by the year 2009. It is estimated that a full third of all of the oil rigs in the Gulf of Mexico, which represent 20% of all deepwater oil rigs worldwide, are drilling to a depth in excess of 5,000 feet (1,524 meters).
The technology for deepwater drilling is not entirely proven, however, as evidenced by one of the largest oil spills in world history. The Deepwater Horizon accident of April 2010 spilled an estimated 205,800,000 gallons (779,037,745 liters) of oil into the Gulf of Mexico, or roughly about half the amount of oil that the US buys from foreign suppliers every day. The Deepwater Horizon drilling rig was authorized by the US government to drill to a depth of 18,000 feet (5,486 meters), but evidence exists that the company was actually drilling to a depth of 25,000 feet (7,620 meters) when the accident took place.
Petroleum production continues to trend towards deepwater drilling, however, with most ultra-deepwater rigs pumping at full capacity while up to 50% of shallow-water rigs at major oil exploration firms have been idled. The incredible increase in depth is put into perspective when considering that drilling has taken place in the North Sea region between the UK and European mainland for decades. The shallow-water, fixed-platform North Sea oil fields, which are considered to be fully exploited, are on average only drilled to a depth of 328 feet (100 meters) and deepwater drilling at the time that they were in full production was considered to be anything at a depth of 500 feet (152 meters) or more.